In general, MIP6 (Mobile IPv6), which is one of the mobile internet protocols, is a technology for supporting movement in an internet protocol version 6 (hereinafter, referred to as IPv6) network. The IPv6, which is the next version of the internet protocol version 4 (hereinafter, referred to as IPv4) that has been used for an internet transfer protocol, has been nearly standardized by the internet engineering task force (IETF). A general MIP6 operation where a mobile node moves from this IPv6 network to other networks will be described in detail.
As shown in accompanying FIG. 1, the mobile node 101 is connected to a home network 110 via an access router. An address allocated in an interface of the mobile node that is connected to a home agent 111 in the home network 110 is referred to as a home address (hereinafter, referred to as HoA), and the home address becomes an address of the mobile node that will be used in an application layer of the mobile node 101.
When the mobile node 101 is disconnected with the home network 110 and connected to a new network 120, the mobile node 101 generates a care of address (hereinafter, referred to as CoA) in the new network 120 and allocates an interface that will be connected to an access router (AR) 121 of the new network, as shown in the accompanying FIG. 2. Then, the mobile node 101 informs the address (CoA) to a home agent 111 through a binding update (BU) message. Therefore, the home agent 111 transfers traffic, which comes to a HoA address, to the CoA through an IPv6 over IPv6 tunnel 20. Then, the mobile node 101 intactly transfers a packet received from a tunnel to an application. However, the mobile node 101 always communicates with a correspondent node (CN) 102 only through the home agent 111 since its path optimization process is not achieved in this state.
Accordingly, the mobile node 101 directly communicates with the correspondent node 102 through the path optimization process without passing through the home agent 111, as shown in the accompanying FIG. 3. In this path optimization process, the mobile node 101 transmits a BU message to a correspondent node 102 to allow the correspondent node 102 to directly transfer a packet to the CoA in the future. The packet, which has transmitted the CoA to its destination as described above, is received in the mobile node 101, and then converts a destination address into a HoA and transfers the converted HoA to an application before the mobile node 101 finally transfers a packet to the application in order to maintain the connection in an application level.
The above-mentioned general operation of the MIP is performed on the assumption that the MIP is entirely operated in the IPv6 networks.
However, the IPv4 has been used in the internet addressing system since it is still not completely changed into the IPv6. Such change of the IPv4 into the IPv6 network may not occur in a moment, and therefore it is expected that the IPv4 and IPv6 networks will be used together for a long time. Therefore, the case that the IPv4 network and the IPv6 network are used in a mixed state should be surely considered to make an application of the MIP6 that stands on the basis of the IPv6 network.
However, in case a mobile node moved to an IPv4 network, it is difficult to ensure the operation of the mobile node in the IPv4 network using the MIP6 protocol that is on the assumption of the operation in the IPv6 network. Therefore, there has been required an automatic tunneling method where a mobile node may pass through the IPv4 network and then maintain the connecting with the original IPv6 network.